Again, until you two can exhibit even a basic knowledge of the Catechism, you shouldn't be posting.
So you're claiming that people can commit mortal sins (that result in the loss of sanctifying grace) without knowing that what they're doing constitutes grave matter? Idiotic.
Now, the natural law is written in men's hearts, so they know about those laws that way, but any positive law (divine or ecclesiastical) requires knowledge. There can be culpability in not doing the necessary diligence to inquire about the law, but some people are in a state where they don't know that they don't know.
From the quote
1859 Mortal sin requires full knowledge and complete consent.
It presupposes knowledge of the sinful character of the act, of its opposition to God's law. It also implies a consent sufficiently deliberate to be a personal choice
I will give an example.
If a man knows drinking lots of alcohol will get him drunk, and he chooses to get drunk, but he doesn't know drunkenness is a grave sin, he has still committed a mortal sin.
Because he knew drinking a lot would get him drunk - so he had full knowledge
He willingly chose to get drunk - he had sufficient deliberate consent
Drunkenness - grave matter
He had all 3 so it would be a mortal sin, even if he didn't know getting drunk was a sin, as the catechism states
"It presupposes knowledge of the sinful character of the act,"
This is how I understand what the catechism teaches.